The invention relates to a method and apparatus for monitoring the switching process of a coupling device for inlet valves and outlet valves of an internal combustion engine.
European patent EP 0 265 281 discloses a device in which a monitoring device for detecting the position of the coupling device is provided. For this purpose, a second pressure line in which a pressure sensor is arranged, an opening which connects the second pressure line to the bore of the coupling device and recesses on the piston of the coupling device are provided. The piston, in an uncoupled position of the coupling device, enabling pressure medium to flow out of the second pressure line via the recesses and sealing the opening in the coupled position. Thus, the position of the coupling device can be determined from the pressure applied.
This arrangement has the disadvantage that a second pressure line is necessary. In addition, with a multi-cylinder internal combustion engine it is not possible to determine at which coupling device a fault occurs.
In addition, European patent EP 0 293 209 discloses a monitoring device with electrical proximity sensors. However, this arrangement is very complex and therefore expensive.
Therefore, the invention is based on the object of providing an operating method for a monitoring device and a monitoring device which is of simple design and arranged on a coupling device, by means of which can be reliably detected whether the bolt has reached the coupled position.
The method according to the invention has the advantage that no additional pressure line and also no additional bores and recesses on the coupling device are necessary. In comparison with the previously known coupling devices, only a pressure sensor which can be arranged at an easily accessible point in the pressure line which is necessary for controlling the coupling device and an evaluation device for evaluating the detected pressure signal has to be provided. The evaluation device detects here the reaching of the coupled position by the occurrence of a pressure surge in the control line which is brought about by the striking of the bolt against the stop.
A further simplification of certain preferred embodiments also consists in the fact that a plurality of coupling devices, which can also be arranged in different cylinders of the internal combustion engine, can be monitored by a single pressure sensor and a single evaluation device.
Since the enabling of the control line and the striking of the corresponding bolt against the stop are chronologically correlated, by virtue of the fact that the pressure signal is evaluated only within a predetermined time after the enabling of the pressure control line, interference signals can be reduced which can result for example from reflection of the pressure surges. At the same time, the influence which the temperature or the switching pressure of the hydraulic medium have on the time which the bolt requires to reach the coupled position can be taken into account by the provision of temperature-dependent time periods T.sub.1 and T.sub.2.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.